270 



OHIO BIOLOGICAL 8URYEY 



The frequent association of the sweet birch (B. lenta) with the 

 hemlock seems to be due to the similarities in their root systems. The 

 seedlings do not develop a tap root, but form a much-branched system 

 of fibrous roots, which spread out freely near the surface, never attain- 

 ing any great depth. They are therefore especially suited to rocky 

 situations in which penetration is difficult or impossible, and they are 



Fig. 12. A Cascade in the Hemlock Forest. 



limited to substrata furnishing a constant supply of water near the 

 surface. Very few soils, however, can maintain such a condition except 

 when bathed in a heavily moisture-laden atmosphei-e. In such humid 

 habitats both species do well regardless of the substrata, growing almost 

 everywhere and shoAving a strong tendency to become epiphytes. But 



